Return bend heat exchanger and process for manufacture



May 22, 1956 R. w. EARL, JR

RETURN BEND HEAT EXCHANGER AND PROCESS FOR MANUFACTURE 2 Sheets-Sheet 1 Filed June 11, 1953 INVENTOR. RALPH W.EARL .JR.

ATTY

May 22, 1956 R. w. EARL, JR 2,746,727

RETURN BEND HEAT EXCHANGER AND PROCESS FOR MANUFACTURE Filed June 11, 1953 2 Sheets-Sheet 2 INVENTOR. RALPH W. EARL JR.

MO M MM ATTY.

United States Patent RETURN BEND HEAT EXCHANGER AND PROCESS FOR MANUFACTURE Ralph W. Earl, Jr., Scottsdale, Ariz.

Application June 11, 1953, Serial No. 360,914

7 Claims. (Cl. 257-255) This invention pertains to a method of forming a return bend heat exchanger from thin walled tubing and to a water storage heat exchanger which is the product of the method.

One of the objects is to provide a method for forming a heat exchanger from a length of tubing so that straight lengths of tubing constitute liquid storage chambers and the return bends at the ends of these chambers are formed throughout an arc of 180 degrees so that each chamber lies parallel to the adjacent chamber.

Another object of the invention provides a method of forming return bends in thin walled tubing which form 180 degree bends, compressing the walls of the tubing somewhat but providing adequate flow as desired.

Another object is to provide a means for quickly and efficiently forming a heat transfer cooler which will contain a quantity of water and permit the passage of water I A still further object is to provide a method for form- 'is merely constricted.

Still another object is to provide a heat transfer radiator and fluid storage device formed of a single length of thin walled tubing consistingof straight portions of tubing connected by integral 180 degrees return bends.

Other objects will appear hereinafter.

I attain the foregoing objects by means of the apparatus, structures, and combination of parts shown in the accompanying drawings, in which- Figure 1 is a side elevational view of a forming. plate showing a length of tubing in the process of being formed thereon into a heat transfer and storage element;

Figure 2 is a plan view thereof showing the first operation in the forming of said heat transfer unit;

Figure 3 is a plan view thereof showing the second operation in the forming of said unit;

Figure 4 is a section taken transversely through said plate substantially on lines 4-4, Figure 1, and drawn on an enlarged scale;

Figure 5 is a plan view of a portion of said forming plate drawn on an enlarged scale;

Figure 6 is a plan view of a heat transfer unit produced by the method herein concerned and drawn on a reduced scale; and

Figure 7 is an end view of said unit.

Similar numerals refer to similar parts in the several views.

In addition to the devices shown in the drawings above mentioned, the method herein concerned is carried out as vhereinafter set forth in detail.

2,746,727 Patented May 22, 1956 A length of thin-walled copper tubing 2 is first threaded at 3 on the starting end 4 and a cap 5 screwed on to this end. Form plate 8 is provided with a U shaped stop 10 at its upper left hand corner, as viewed in Figures 1 and 5 and with holes 12 equally spaced and aligned along each side thereof. Return bend forming pins 14 are inserted in several holes 12 as the forming process proceeds. Each of these forming pins consists of a cylindrical shaft 16 having a disk shaped head 17 at its upper end and a shoulder 18 at its lower end. Below the shoulder the shaft has a reduced portion 20 which extends through and below plate 8. A transverse slot 21 is formed in the lower end portion of the shaft to receive wedge 23. Each of the forming pins is made the same and each fits into one of the several holes 12. When the lower portion 20 of one of the pins is inserted in hole 12 wedge 23 holds the pin down against shoulder 18 and forms an easily removable means for retaining the pin in the hole and for maintaining the distance between the top face 28 of plate 8 and the under face 29 of head 17 in definite spaced relation.

After tube 2 has been placed in yoke 10 the plate 8 is rotated, using handle 45, relative to the axis of tube 2 y'so as to bring it against and around first pin 14, marked straight length of thetubing adjacent yoke 10 and marked C. This motion of the plate forms a return bend E around pin A. I have found that if the distance between the top face of the plate and'the under face of head 17 bears a substantially definite relation to the diameter of tubing 2, which is not greater than per cent more than the diameter and not less than 10 per cent more than the diameter, a bend having a section as shown in Figure 4' and designated E will be produced. In this bend it is to be noted that the inner wall' 30 is concave rather than convex in shape, as in the tube before bending, likewise the outer wall 32 of the bend is concave. The top and bottom faces 33 of the bend are fiat and parallel to each other. Substantially triangularly shaped openings 35 are formed adjacenteach top and bottom edge and are bounded by the concave inner and outer wall portions of the tube and their adjacent flat sides 33. These openings, while they have a decidedly less cross section area than that. of the tube originally may be entirely adequate to carry a flow of water through the heat transfer unit.

After the forming on the, first bend E, a second bend H between straight lengths B, and G of the tube is formed over pin I which is' insertedand wedged in the first hole below yoke 10 along the'left side of plate 8. In Figure 5' the tubing 2 is shown in contact with a third pin K just before being bent by-a counter-clockwise rotational movement of plate 3. A bendsimilar to E is then formed at K in the manner above described. This process of (a) setting and wedging pins into plate 8, and (b) rotating the plate so as to bend the tubing around the pins, and (c) confining the top and bottom wall portions 33 between surfaces 28 and 29, is continued until a zig zag return bend unit is formed as shown in Figure 6.

It will be noted that the two side walls 32 and 30 of each bend are compressed together and in contact. Due to this fact there is a minimum of stretching of the metal on the outer side wall 32 relative to the inner side wall 30. The confining of the top and bottom faces of the bend between the surfaces 28 and 29 forces the top and bottom faces 33 to take a flat shape as the bending movement proceeds. If these walls are not confined the tube will be entirely and completely flattened and no open areas 35 will be produced. If these surfaces are closer together than the amounts above specified then the outer edges 37 of the upper and lower bends will be stretched so much that fracture or other failure of the metal is likely when pressure is applied to the interior of tube 2. From the foregoing it will be seen that the crushing effect of the sharp bend must be confined within somewhat critical limits in order to secure the structure shown.

After the device has been formed, as above mentioned. wedges 23 and all pins 14 are removed. The several straight sections B, C, G and the like, may then be compressed somewhat and secured in place by head caps 40 thus forming the heat transfer unit 50. A cap similar to may be added at the finish end 41 and inlet and outlet tubes 42 and 43, respectively, may be threaded into or otherwise secured to these caps.

The entire device 50 when installed in a refrigerator will take the place of the ordinary metal wire shelf used in standard refrigerators. Water under pressure may be let into the device through fitting 42 and removed through fitting 43. The straight lengths of tubing C, B, G, etc., between the return bends then act as water storage chambers and will cool water contained therein from the refrigeration in the refrigerator box. This water may be drawn from these storage spaces through fitting 41 which has an interior cross sectional area substantially the same as that of the combined interior cross sectional areas 35 of any of the several return bends.

A unit 50 made with return bends, as above described, may be constructed with a maximum number of straight lengths of tubing closely compacted in parallel relation. Return bends formed in this tubing, as above described, can be easily, quickly and cheaply made and serve the purpose intended by joining the several storage chambers. No welded or soldered joints are necessary in the construction of this unit and fracture of the tubing from freezing or usual water pressure is extremely unlikely.

To produce a bend of the type desired several conditions must be met. First, the tubing should be of the type called thin walled medium hard; second the cylinder 16 of the pin 14 should be approximately one-half the diameter of the tube 2; third, the tube must be restrained from longitudinal movement during the bending either by cap 5 held against yoke 10, or by making the first bend in the middle of the tube and continuing each way therefrom around pins 14; fourth, the sides or checks of the tube 2, indicated at 33 and being at right angles to the axis of pin 14, and to the axis of the bend, must be allowed to expand somewhat beyond the diameter of the tube but must be confined from expansion beyond to 25 percent of the diameter of the tube.

When bends are made under the above conditions the section shown in Figure 4 is formed and the tube is not completely crushed, nor it is weakened.

Once the jig or bending plate is made the process be comes cheap, accurate, and rapid, and the resulting product is efficient for the purposes intended.

I claim:

1. The method of forming a heat exchanger having parallel straight lengths of tubing forming tubular storage chambers arranged in a single plane and joined by return bends formed in the tubing by bending the tubing at predetermined intervals through an angle of approximately 180 and confining the sides of the tubing at right angles to the axis of the bend to an expanding distance apart not greater than 125% of the diameter of the tubing nor less than 110% of the diameter of the tubing, thereby forming a bend having triangular shaped duct portions adjacent said confined sides of constricted cross sectional area relative to the cross sectional area of said straight lengths of tubing.

2. In the manufacture of heat exchangers consisting of straight lengths of round metal tubing connected by tight return bends of approximately 180 in zig zag fashion,

the process of forming tight return bends between said straight lengths of tubing consisting of bending the tubing around a cylinder and confining the sides of the tubing at right angles to the axis of said cylinder to confine spreading of tubing parallel to the axis of the bend to a distance 25% greater than the diameter of the tubing, thereby forming bent ducts of substantially triangular section adjacent each of said confined sides of said tubing.

3. In the manufacture of heat exchangers consisting of straight lengths of round metal tubing connected by tight return bends of approximately 180 in zig zag fashion, the process of forming tight return bends between said straight lengths of tubing consisting of bending the tubing around a cylinder, and confining the sides of the tubing at right angles to the axis of the bend between flat plates during the bending so that said confined sides will not expand a distance greater than 25% of the diameter of the tubing and will form flat surfaces, andthe sides of the tubing concentric with the bend will assume concave cross-sectional shapes, and arcuate passage ways of substantially triangular section will be formed on each side of the tubing adjacent said fiat surfaces.

4. A heat exchanger composed of a single piece of round tubing bent at intervals forming a zig zag return bend structure, each of said return bends having a compass of 180 and having flattened sides at right angles to the axis of the bend, more than of the diameter of the tube apart, and not greater than of the diameter of tube tube apart, the sides of the bend concentric with the axis of the bend being concave, and forming, together with said flattened sides, arcuate passage ways having substantially triangular sections.

5. The method of forming a heat exchanger having parallel straight lengths of tubing forming tubular storage chambers arranged in a single plane and joined by return bends formed in the tubing consisting of forming degree bends in thin walled medium hard metal tubing at pre-determined intervals by bending said tubing over cylindrical surfaces having diameters equal to one-half the diameter of the tube being bent, holding the tube against longitudinal movement, and confining the sides of said tube at right angles to the axis of the bend to an expansion not greater than twenty five per cent of the diameter of the tube.

6. In the manufacture of heat exchangers consisting of straight lengths of round metal tubing connected by tight return bends of approximately 180 degrees in zig zag fashion, the process of forming tight return bends between said straight lengths of tubing consisting of bending the tubing around a cylinder having a diameter equal to one half of the diameter of the tubing and confining the sides of the tubing at right angles to the axis of the bend to limit spreading of the tubing parallel to the axis of the bend to a distance not greater than twenty five per cent of the diameter of the tubing, thus forming bent ducts of substantially triangular sections adjacent each of said confined sides of said tubing while the curved sides of said tubing around each bend are formed to have concave cross-sections; said tubing being held to prevent longitudinal movement while being bent.

7. In the manufacture of heat exchangers consisting of straight lengths of round half hard thin walled copper tubing connected by tight return bends arranged in zig zag fashion, the process of forming tight return bends between said straight lengths of tubing consisting of bending the tubing around a cylindrical surface having a diameter equal to one half that of said tubing forming a bend of approximately 180 degrees, and confining the sides of the tubing at right angles to the axis of the bend between fiat surfaces during the bending so that said confined sides will expand a distance parallel to the axis of said cylindrical surface equal to 10 to 25 per cent of the original diameter of the tubing and form flat faces, and the sides of the tubing concentric of the bend assume concave References Cited in the file of this patent UNITED STATES PATENTS 6,929 Du Trembley Dec. 4, 1849 169,392 Wicks NOV. 2, 1875 Smith Aug. 4, 1903 Kennedy Nov. 14, 1905 Merritt et a1 Feb. 20, 1917 Scott Jan. 6, 1931 Bilyeu Dec. 9, 1947 Skinner July 26, 1949 Stringfield June 19, 1951 Jennings Sept. 1, 1953 

